It is well known that exposure to the sun, sunlamps, or other tanning means to which individuals subject themselves also exposes such individuals to ultraviolet radiations between the wavelengths of about 280 millimicrons to about 320 millimicrons which are responsible for distressing burning and reddening (erythema) which is suffered by overexposure to such tanning means. In order to permit tanning without burning so-called sunscreening compositions have been made commercially available to diminish or avoid discomforts and dangers of erythema which may be produced. These compositions are adapted to be applied to the body areas which are to be exposed for tanning and their formulations generally contain a compound which can absorb ultraviolet radiation in the range of from about 280 to 320 millimicrons and thus alleviate the problems of erythema.
As is known, an effective sunscreening preparation essentially performs two functions. The first and most important is to protect the user from burning, blistering and injurious effects of prolonged exposure to sunlight. The second function is to permit the most rapid possible development of the skin pigmentation or tanning. As noted above, the erythemal range from which protection is sought lies between about 280 and 320 millimicron units. It is generally agreed that effective, relatively rapid tanning, without painful erythema results from exposure of the skin to radiation from about 320 to about 420 millimicron units. An effective suntan preparation is thus one which selectively absorbs or screens the erythema rays and permits transmission of the tanning rays above the 320 millimicron range.
It has been known that various aminobenzoic acid derivatives have sunscreening properties. These include the derivatives of ortho and para-aminobenzoic acid such as the dimethylaminobenzoic acids which have been used in the past in suntanning preparations. It is also known that esters of ortho- and para-aminobenzoic acid, such as the methyl, ethyl or propyl benzoates, as well as those esters from higher alkyl alcohols have valuable sunscreening effects. Such compounds, while having desirable properties, have been found not ideally suited for the purpose intended. They lack one or more of such desirable characteristics as insolubility in water, nonstaining of fabrics, stability on storage, stability on exposure to ultraviolet or visible radiation, resistance to air oxidation, solubility in cosmetic carriers at low temperatures, such as room temperature, and substantiveness to the skin.
The majority of the sunscreening compounds known heretofore lack the essential characteristic of being substantive to the skin. The majority of compounds, when topically applied in the various known forms, have been easily removed from the skin by salt or fresh water or through the action of perspiration of the user. In as much as sunscreening compositions are generally used in hot weather and at beaches and water facilities where people enjoy bathing activities, such compositions which are removed by water have limited effectiveness. Even where artificially induced rays, such as by commercially available sunlamps, are used the heat causes the user to perspire which, in turn, washes away the sunscreening agents.